Oscillators are a critical piece of many electronic circuits, producing clean periodic clock signals to drive microcontrollers, as timing references in analog and RF circuits, and elsewhere. As ubiquitous as they are, however, they remain a niche topic, with minimal coverage from many of the large hobbyist electronics sites and communities.
Enter YouTube user devttys0, with an excellent deep dive into the world of analog electronics. His video on Pierce Oscillator fundamentals is posted below. For even more analog goodness, be sure to take a look at his website, Analog Zoo.